Disc drive data storage devices are commonly used as the primary data storage and retrieval devices in modern computer systems. In a typical disc drive, data are magnetically stored on one or more discs that are rotated by a spindle motor at a constant high speed. The discs are accessed by a rotary actuator assembly having a corresponding number of read/write heads that fly adjacent the respective surfaces of the discs.
The discs are axially aligned and stacked about a spindle motor hub. Typically, one or more disc spacers are interleaved with the discs to form a disc/spacer stack, with the spacers serving to provide the various discs with the desired axial spacing within the stack. Once completed, a disc clamp is installed to secure the disc/spacer stack to the spindle motor hub. The assembled spindle motor hub, disc(s), spacer(s) and clamp is collectively referred to as a “disc stack assembly.”
Disc drives are formed in highly automated manufacturing environments. A pallet system is typically employed wherein a pallet (tray) is provided for the assembly of each disc drive. The pallet is provided with an initial set of articles (such as a base deck) and the pallet is moved along a conveyor system to a succession of assembly stations wherein articles are added to form the drive.
In the current generation, automated assembly stations that build disc stack assemblies-place one article at a time onto the spindle motor hub. For example, a first robotic arm is manipulated to place a first disc onto the hub and then a second robotic arm places a first spacer onto the first disc. These operations are repeated until the final desired total numbers of discs and spacers have been added to the stack. The time to complete the stack is proportional to the number of discs in the stack.
A problem with this approach is that other assembly stations (such as a head merge station wherein the actuator is merged with the disc stack assembly) do not have cycle times that depend on the number of discs in the stack. The result is that the disc stack assembly station can induce a bottleneck, or line slowdown, in the flow of pallets through the assembly process. Similar bottlenecks can be observed in other types of automated processing lines that handle other types of stacked articles.
Additional delays in the assembly process due to the existing configuration of disc stack assembly stations relate to the use of conventional vacuum chuck type end effectors which apply a vacuum to grasp and release the discs and spacers. Such end effectors require precise planar alignment with the associated disc or spacer feeder and are susceptible to damage such as scratches on the articles which can prevent formation of a reliable vacuum seal. Also, there is a small amount of latency time required for the creation and the release of the vacuum; this latency time is required for each spacer and disc added to the stack and can add up to a significant amount of time when a large number of discs and spacers are employed in the stack.
Accordingly, there is a need for improvements in the art for more efficient assembly of stacked articles, such as discs and spacers, in an automated assembly process.